1. Field of the Invention
The present invention relates to a method of fabricating a liquid crystal display device, and particularly, to a method of fabricating a liquid crystal display panel capable of preventing rubbing from being abnormally made due to a step difference by disposing liquid crystal display panels of various sizes with their pixel parts made to correspond to one side.
2. Description of the Related Art
In recent information society, a display is considered to be more and more important as a visual information transmission media. In order to occupy a major position in the future, the display has to satisfy a low power consumption characteristic, a thin and light characteristic, a high picture quality characteristic, etc. Because a liquid crystal display (LCD) device (a major product of a flat panel display (FPD)) is equipped with not only functions to satisfy said conditions but also with a mass production characteristic, various kinds of new products using the LCD device are rapidly being invented, and the LCD device has become a core component which can replace the existing cathode ray tube (CRT).
A general liquid crystal display device displays an image by controlling light transmittance by using an electric field. To this end, the liquid crystal display device includes a liquid crystal display panel including a driving circuit part, a backlight part installed at a lower portion of the liquid crystal display panel, a mold frame for supporting the backlight part and the liquid crystal display panel, and a case.
Hereinafter, a general liquid crystal display panel will now be described in detail with reference to FIG. 1.
FIG. 1 is a plan view roughly showing a structure of a general liquid crystal display panel.
As shown therein, the liquid crystal display panel 10 largely includes an array substrate 20, a color filter substrate 30 and a liquid crystal layer formed between the array substrate 20 and the color filter substrate 30.
The array substrate 20 includes a plurality of gate lines 21 and a plurality of data lines 22 that define a plurality of pixel regions 25 by being arranged vertically and horizontally on the substrate 20, a plurality of thin film transistors (TFTs) each formed at an intersection of the corresponding gate line 21 and the corresponding data line 22 and a plurality of pixel electrodes formed in the pixel regions 25.
Here, the array substrate 20 has a region along a long side and a region along a short side that protrude beyond the color filter substrate 30 so that the driving circuit unit for driving the liquid crystal display panel is positioned thereto. Particularly, a gate pad part 24 is formed in the region along the short side region of the array substrate 20, and a data pad part 23 is formed in the region along the long side region of the array substrate 20.
In addition, the gate pad part 24 supplies a scanning signal, which is supplied from a gate driving circuit part (not shown), to the gate line 21 of each pixel region 25 of the pixel part, an image-displayed region. The data pad part 23 supplies image information, which is supplied from a data driving circuit part (not shown), to a data line 22 of the pixel region 25.
Even though it is not shown in FIG. 1, a color filter for implementing colors and a common electrode facing the pixel electrodes formed on the array substrate 20 are formed at an image-displayed region of the color filter substrate 30.
The array substrate 20 and the color filter substrate 30 constructed as above face each other and are attached by a sealant (not shown) formed along an outer edge of the image-displayed region. The attachment of the two substrates is made through an attachment key (not shown) formed at the array substrate 20 or the color filter substrate 30.
This process of fabricating the liquid crystal display device can be divided into an array substrate process for forming a switching device on an array substrate, a color filter substrate process for forming a color filter on a color filter substrate and a cell process. The process for fabricating the liquid crystal display device will now be described with reference to FIG. 2.
First, a plurality of gate lines and a plurality of data lines are arranged vertically and horizontally on a transparent insulation substrate such as glass to thereby define a plurality of pixel regions, and a thin film transistor (a switching element) connected to the corresponding gate line and the corresponding data line, is formed at each pixel region (S101). In addition, a pixel electrode connected to the corresponding thin film transistor and driving a liquid crystal layer as a signal is applied thereto through the thin film transistor, is formed at each pixel region through the array substrate process (S101).
In addition, a color filter including sub-color filters (R, G, B) for implementing colors, a black matrix for isolating the sub color filter from other sub color filters and cutting off light transmitted by a liquid crystal layer and a transparent common electrode corresponding to the pixel electrode are formed on the color filter substrate by the color filter substrate process (S104).
Then, alignment layers are applied over the array substrate and the color filter substrate, respectively, and then the alignment layers are rubbed in order to provide an alignment controlling force or a surface anchoring force (i.e., pretilt angle and alignment direction) to the liquid crystal molecules of the liquid crystal layer formed between the array and color filter substrates (S102, S105).
Next, spacers for maintaining a uniform cell gap are dispersed onto the array substrate, a sealing material is applied along an outer edge portion of the color filter substrate, and then the array substrate and the color filter substrate are attached by applying pressure thereto (S103, S106, S107).
At steps S101 and S104, the array substrate and the color filter substrate are formed respectively on large-sized mother glasses (i.e., mother substrates). Namely, a plurality of panel regions are formed on the large-sized mother substrate and a plurality of thin film transistors which are switching devices or a color filter layer are respectively formed at the panel regions. Therefore, in order to fabricate individual liquid crystal display panels, the mother substrates that are attached at step S107 are cut and processed to form individual liquid crystal display panels (S108).
Thereafter, a liquid crystal material is injected into each of the individual processed liquid crystal display panels through a liquid crystal injection opening, then the liquid crystal injection opening is encapsulated to form the liquid crystal layer, and finally, the injected liquid crystal display panel is tested, thereby completing the liquid crystal display panel (S109, S110).
In fabricating such a liquid crystal display panel, in order to improve productivity, a method of simultaneously disposing a plurality of unit liquid crystal display panels on a large-sized mother substrate is generally being used.
FIG. 3A is a view showing that a plurality of liquid crystal display panel regions in one same size are disposed on a mother substrate, and FIG. 3B is a view showing that liquid crystal display panel regions in one bigger same size are disposed on the mother substrate compared to the panel regions of FIG. 3A.
FIG. 3A shows a case that six liquid crystal display panel regions are disposed at regular intervals, considering the size of the mother substrate and the size of the liquid crystal display panels to be formed. That is, as shown therein, six first liquid crystal display panel regions 10a having the same size are disposed on the mother substrate 40. A TFT array substrate or a color filter substrate is formed at each region 10a. 
Once the mother substrate having the array substrates and the mother substrate having the color filter substrates are attached to each other to form first liquid crystal display panels and then processed to separate the first liquid crystal display panels, leaving behind a region of the mother substrates where the liquid crystal display panels are not formed and which is discarded after the separation. Accordingly, preferably, the first liquid crystal display panels are disposed to minimize the region where the liquid crystal display panels are not formed and to maximize the number of liquid crystal display panel regions provided on the mother substrates.
Here, each first liquid crystal display panel region 10a having the array substrate or the color filter substrate has to pass through a rubbing process in order to provide an alignment controlling force to liquid crystal molecules. In the drawing, a case that the rubbing is made in an arrow direction regardless of a driving mode of a liquid crystal display panel (i.e., Twisted Nematic; TN) mode, an In-Plane Switching (IPS) mode or a S (super)-IPS mode, is depicted.
For an additional reference, a liquid crystal display panel is a display device for displaying an image by controlling the amount of light transmitted by a liquid crystal layer. The transmission level is controlled by an initial alignment state of the liquid crystal molecules having a double refraction property and by driving the liquid crystal molecules according to a signal. Driving modes of a liquid crystal display panel are determined by an initial alignment direction and the method of driving the liquid crystal molecules. Namely, because liquid crystal display panels with different modes have different initial alignment directions, the directions of the alignment layers have to be different.
Therefore, panel regions with different modes, which are formed on a substrate (array substrate and color filter substrate), have to be rubbed in different directions.
In addition, because a main viewing angle of the fabricated first liquid crystal display panel is determined according to a direction of rubbing made on the mother substrate 40, the panel regions 10a have to be disposed in the same direction in order to simultaneously fabricate the plurality of liquid crystal display panels having the same main viewing angle.
In case of fabricating bigger-sized liquid crystal display panels on the same mother substrate of FIG. 3A, only two second liquid crystal display panel regions 10b of the same size can be disposed on each mother substrate 40 as shown in FIG. 3B, and a region of the mother substrate 40 where the second liquid crystal display panel regions 10b are not disposed has to be discarded subsequently.
Accordingly, as the size of the liquid crystal display panels increases, the efficiency of using the mother substrate is deteriorated, which deteriorates productivity and increases product cost.
Here, when the second liquid crystal display panel regions 10b having the array substrate/color filter substrate are disposed as shown in the drawing, rubbing has to be made in a direction perpendicular to the direction of rubbing depicted in FIG. 3A. The arrangement direction of the array substrates and the color filter substrates on the mother substrates are made without regard to their pixel parts.
In general, a plurality of liquid crystal display panels (e.g., four, six, eight or sixteen liquid crystal display panels) are formed on a mother substrate and a technique for forming the plurality of liquid crystal display panels on the mother substrate are considered to be a main factor that determines fabrication efficiency of the liquid crystal display panel. Accordingly, researches on the techniques for efficiently using a mother substrate are actively ongoing, and these techniques affect competitiveness of liquid crystal display device manufacturers.
However, the size of the mother substrate 40 is standardized and depends on the size of the liquid crystal display panel being fabricated. Namely, the standard size of the mother substrate is set so that the mother substrate has an area to efficiently fabricate the liquid crystal display panels. As such, as shown in FIG. 3B, if a liquid crystal display panel with a different size is fabricated on the standard sized mother substrate, a large region of the mother substrate remains unused. This problem may be solved by forming the liquid crystal display panel on a mother substrate with a standard sized corresponding to the liquid crystal display panel to be made. But, there is no mother substrate that is standardized according to the liquid crystal display panel to be made, so the liquid crystal display panel must be formed on a mother substrate with a different standard as shown in FIG. 3B. Accordingly, a large portion of the mother substrate remains unused and the unused region of the mother substrate is discarded, thereby increasing the fabrication cost of the liquid crystal display panel.
In addition, if a plurality of liquid crystal display panels are disposed on the mother substrate, randomly (without any regular directionality) in order to improve the efficiency of using the mother substrate, the surface of the panel may be easily damaged during a rubbing process. That is, if a rubbing is made on the substrate on which a plurality of liquid crystal panels are disposed randomly, a blotted region may be generated due to a step difference because positions where rubbing is started and completed are varied according to the liquid crystal display panels.